The presently described embodiments relate to a thin film or thick film heater and control architecture for an ink jet liquid drop ejector. They find particular application in conjunction with ink jet liquid drop ejector (known in the art as print heads) useful for emitting phase change inks, and will be described with particular reference thereto. However, it is to be appreciated that the presently described embodiments are also amenable to other like applications where liquid material can be ejected with the benefit of ejector temperature regulation. Such liquid jettable material can be ink jet printer ink, liquid metal, color filter material, photoresist material, curable resin, bio-reagents or even chocolate (food) etc.
By way of background, different types of droplet ejectors are known. Selective applications shall be reviewed here for illustration purposes. U.S. Pat. No. 6,007,183 (Dec. 28, 1999) entitled “Acoustic Metal Jet Fabrication using an Inert Gas”, U.S. Pat. No. 6,019,814 (Feb. 1, 2000) entitled “Method of Manufacturing 3D Parts using a Sacrificial Material”, U.S. Pat. No. 6,248,151 (Jun. 19, 2001) entitled “Method of Manufacturing Three Dimensional Parts using an Inert Gas” and U.S. Pat. No. 6,350,405 (Feb. 26, 2002) entitled “Apparatus for Manufacturing Three Dimensional Parts using an Inert Gas”, all to Horine, describe liquid drop ejectors which ejects liquid metal, such as hot solder and other similar material to make 3D parts. U.S. Pat. No. 6,416,164 (Jul. 9, 2002) to Stearns et al., entitled “Acoustic Ejection of Fluids using Large F-Number Focusing Elements”, U.S. Pat. No. 6,548,308 (Apr. 15, 2003) to Ellson et al., entitled “Focused Acoustic Energy Method and Device for Generating Droplets of Immiscible Fluids”, and, U.S. Pat. No. 6,612,686 (Sep. 2, 2003) to Mutz et al. entitled “Focused Acoustic Energy in the Preparation and Screening of Combinatorial Libraries” are application examples where bio-reagents can be ejected from a liquid drop ejector. U.S. Pat. No. 6,742,884 (Jun. 1, 2004) to Wong et al., entitled “Apparatus for Printing Etch Masks using Phase-change Materials” is an example of printing phase change materials for the purpose of fabricating electronic circuit and devices. U.S. Pat. No. 5,989,757 (Nov. 23, 1999) entitled “Color Filter Manufacturing Method” and U.S. Pat. No. 6,720,119 (Jul. 6, 2004) to Ito et al., entitled “System and Methods for Manufacturing a Color Filter using a Scanning Ink Jet Head” describe methods of using an ink jet liquid drop ejector to eject color filter material. U.S. Pat. No. 6,561,640 (May 13, 2003) to Young, entitled “Systems and Methods of Printing with Ultraviolet Photosensitive Resin-containing Materials using Light Emitting Devices” and U.S. Pat. No. 6,536,889 (Mar. 25, 2003) to Biegelsen et al. entitled “Systems and Methods for Ejecting or Depositing Substances containing Multiple Photoinitiators” are other examples of ejecting resin-containing materials. These illustrated applications can greatly benefit from the presently described embodiment of integrated thin film or thick film heater and control architecture for such temperature regulated liquid drop ejectors.
The use of heaters on liquid drop ejectors that emit phase change ink is well known. The phase change ink is solid at room temperature and a jettable liquid at about 130 degrees to 140 degree Celsius. This temperature dependent viscosity can affect ink drop ejection velocity which can impact the process direction placement accuracy of ink drops on a rotating drum or substrate medium. A typical ink jet velocity change with temperature is about two to three percent per degree Celsius. Typical viscosity for these phase change ink at jetting temperature is about 10 to 15 centipoise. Several phase change ink drop ejectors with externally attached heater elements and thermistors are known. For example, U.S. Pat. No. 4,418,355 to DeYoung et al, (Nov. 29, 1983) for an “Ink Jet Apparatus with Preloaded Diaphragm and Method of Making Same” describes an early version of a reciprocating ink jet head with an attached heater element and a discrete thermistor temperature sensor. U.S. Pat. No. 5,087,930 to Roy et al. (Feb. 11, 1992) for a “Drop-on-demand Ink Jet Print Head” and U.S. Pat. No. 5,083,143 to Hoffman (Jan. 21, 1992) for “Rotational Adjustment of an Ink Jet Head” provide some background description of a 9.5 cm wide, 96 jets, reciprocating carriage version of such a phase change ink print head.
One embodiment of a full media width phase change ink or liquid drop ejector is disclosed in U.S. Pat. No. 5,424,767 (“the '767 patent”) to Alavizadeh et al. (Jun. 13, 1995) for an “Apparatus and Method for Heating Ink to a Uniform Temperature in a Multiple-orifice Phase-change Ink-jet Print Head”. In this regard, as disclosed in the '767 patent, FIG. 1 is an isometric exploded view showing the positioning of media-width liquid drop ejector 44 relative to liquid drop ejector heater 58, flex circuit 62, ink reservoir 52, ink premelt chambers 54C, 54M, 54Y, and 54K, and cartridge heaters 56. Cartridge heaters 56 are inserted into a heat distribution bar 100 that is assembled in thermal contact with reservoir 52 and ink premelt chambers 54. The temperature of heat distribution bar 100 is sensed by a thermistor 102 (shown in phantom) that, in combination with a conventional zero crossing integer cycle temperature controller, regulates the temperature of heat distribution bar 100, reservoir 52, and premelt chambers 54. Their combined thermal mass is such that the temperature controller has a relatively slow 90 second thermal response time, which is sufficient for ink melting, storage, and distribution purposes.
In contrast, liquid drop ejector 44 employs a faster thermal response time of about three to about seven seconds to respond to temperature changes caused by the above-described thermal transfer mechanisms, printer mode-related temperature changes, and heat lost by ejecting dense ink patterns. The temperature of liquid drop ejector 44 is sensed by a thermistor 104 (shown in phantom) that is inserted into a well in liquid drop ejector 44 and controlled as above by the temperature controller which powers liquid drop ejector heater 58.
Liquid drop ejector 44 is mated to reservoir 52 along a rectangular surface contact region 92 (shown in dashed lines). Contact region 92 on reservoir 52 includes four rows of ink ports 106 through which liquid drop ejector 44 receives melted yellow, magenta, cyan, and black ink. Contact region 92 on printhead 44 includes four rows of mating ink ports (not shown) that are separated from and positioned below four rows of orifices 46. The difference of thermal response times on either side of contact region 92 prevents thermal oscillation between the liquid drop ejector and reservoir-related temperature control loops.
Liquid drop ejector heater 58 is bonded to the rear surface of liquid drop ejector 44 just adjacent to and above contact region 92. A cutout region 108 in liquid drop ejector heater 58 accommodates the area required by the piezoelectric transducers (not shown) that drive rows of orifices 46. The piezoelectric transducers are electrically connected to driver circuits 60 by flex circuit 62.
Alternatively, cutout region 108 can be eliminated if liquid drop ejector heater 58 is bonded to the major surface of flex circuit 62 facing away from printhead 44. In this embodiment, heat from liquid drop ejector heater 58 conducts through flex circuit 62 and into liquid drop ejector 44 in part through the piezoelectric transducers. The piezoelectric transducers are not good heat conductors, but neither is the stainless steel from which liquid drop ejector 44 is made. This embodiment provides a more direct heat conduction path to ink adjacent to each of orifices 46.
Notably, the phase change liquid drop ejector with the attached flexible circuit heater, as disclosed in the '767 patent, has at least some drawbacks. Because the flexible material of the heater is a thermal insulator, and because added thermal contact resistance resides in the assembly, the liquid drop ejector substrate temperature is not as responsive to changes in the flex heater temperature as may be desired. This is a disadvantage for this implementation. Other disadvantages of this configuration include higher manufacturing costs.
Another disadvantage to this type of configuration is that the flexible circuit results in a limited maximum pixel resolution—because the signal lines have inherent constraints.
Moreover, it would be desirable to implement a design that achieves good quality prints using phase change ink liquid drop ejectors. To do so, appropriate heat uniformity across the pixel zone is required.